Electrographic reproduction article and method



Feb. 17, 1970 BENNING 3,496,0 3

} ELECTROGRAPHIC REPRODUCTION ARTICLE AND METHOD Filed Feb. 15, 1966 Fig.

HIGH DENSITY P01. YET/I YLENE 8r PIIOT OSE IVS! T I VE' ZINC OXIDE INSEIVS/ Tl VE SUBS TIM T E Fig. 2

WHITE MASK/N8 LAYER HIGH DENSITY POL YE T H YLE NE 8 CONDUCT I YE CARBON GLA'CK Calvin J. Benn/0g mvsmozz ATTORNEY United States Patent l 3,496,063 ELECTROGRAPHIC REPRODUCTION ARTICLE AND METHOD Calvin J. Benning, Clarksville, Md., assignor to W. R.

Grace & Co., New York, N.Y., a corporation of Connecticut Filed Feb. 15, 1966, Ser. No. 538,118 Int. Cl. B32b 27/30, 27/32 US. Cl. 161-247 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to media upon which images may be reproduced by high-speed electric printers and by electrostatic printing machines.

In an electric printer, the image is formed by an electrical discharge which passes to ground through a bi-color laminated sheet. The discharge burns through or melts away the top layer and exposes the underlying lamination, leaving usually, a black image appearing against a contrasting background.

In electrographic printing, on the other hand, a photo- Sensitive material is incorporated in a coating which is spread upon a paper substrate. It is characteristic of certain materials, notably zinc oxide, that they will accept and retain an electric charge placed on their surface in the dark, but that when exposed to light, the electric charge will be dissipated in all exposed areas. Accordingly, if a sheet coated with, i.e. Zinc oxide, is first charged and then is exposed through an original, the background loses its charge.

As applied to printing, the charged areas Will attract and hold fusible ink particles which either may be brushed or flooded across the surface of the exposed sheet. When the sheet then is heated, the ink clinging to the charged area fuses to the substrate leaving a clear background area on which permanent printed characters appear in contrasting color.

One of the difliculties associated with high-speed electric printing is the control of the through-resistance. In media used in electrographic printers a characteristic difliculty is poor reproduction whenever the media has been exposed to varying humidities before its use. The amount of moisture contained in the substrate materially affects the color and definition of the reproduced image. Ideal storage conditions rarely are found in practice, for ofiices using such reproducing machines must store the reproducing media in any available space.

3,496,063 Patented Feb. 17, 1970 I have discovered that certain compositions containing either a conductive or a photo-sensitive substance may be produced as uniform surface sheets or films which are uniformly electrically responsive, and that such films are Well adapted to form either the surface or the substrate layers of copy sheets for electric printing. I have found, too, that the sheets may be combined to produce composite sheets in a variety of combinations to adapt the sheets for use in the numerous models both of high-speed electric and electrographic printers.

The invention includes all-plastic laminated sheets or sheets in which the electrically responsive plastic compositions are combined either with a conductive or nonconductive paper layer. In all forms the invention presents two main aspects: (a) a substrate for high-speed electric printing in which the through-resistance may be accurately controlled, and (b) a composite sheet which is comparatively insensitive to change in humidity.

In the case of conductive substrates, not only may the initial through-resistance be controlled within reasonable limits, but by subsequent treatment, the resistance may be adjusted to precise values.

In the case of photo-sensitive media, a reproducing surface with lower sensitivity to humidity change may be laminated or spread on a variety of substrates. Several of the many possible combinations of surface and substrate will be set forth in separate examples.

Briefly stated, the present invention comprises a composite copy sheet adapted for use in electric printing apparatus comprising a substrate layer and a coating layer, at least one of said layers being electrically responsive and at least one of said layers being composed essentially of an intimate mixture of high density polyethylene having a standard load melt index of substantially zero, a particulate filler, and a plasticizer.

FIG. 1 illustrates a small cut sample of a sheet suitable for electrographic printing, and

FIG. 2 is a small sample of a sheet suitable for highspeed electric printing. For clarity, the thickness of the individual layers in the sheets has been greatly exaggerated.

The polyethylene used in the present invention should have a standard load melt index of substantially 0 and a high density, i.e. about 0.93 to 0.96.

The filler component of the instant composition, i.e. that comprised of the polyethylene, filler and plasticizer, may be electrically responsive or electrically non-responsive. The electrically responsive filler should be present in sufiicient proportion to impart electrically responsive characteristics to the said sheet. Satisfactory results are produced from electrically responsive compositions comprised of about 15 to 30% of high density polyethylene of standard load melt index of substantially 0, 20 to electrically responsive filler, and 10 to 50% plasticizer.

Representative of the electrically responsive fillers are photo-sensitive zinc oxide and conductive carbon black.

The standard load melt index (SLMI) used herein indicates the rate of extrusion of the polyethylene as measured under the conditions specified in ASTMD 123857T (Condition E). Since a high molecular weight polyolefin is more difiicult to extrude than a low molecular weight 3 4 1 31 a standard load melt index of would indicate The electrical resistivity of the photo-conductive sura very high molecular weight polyolefin. face was greater than 3.88 mho.-cm.- Since the The high load melt index (HLMI) was measured as laminate was comprised of a substrate of plastic composispecified in ASTMD 1238-57T (Condition F). tion relatively insensitive to water, and the photo-sensi- Density was measured according to ASTMD 1505-57T. tive layer included photo-sensitive zinc oxide thoroughly All parts and percentages used herein are by weight 5 embedded in plastic, it was found to withstand a wider unless otherwise specified. range of humidity in the ambient atmosphere and yet EXAMPLE L-PREPARATION OF SUBSTRATE Polymer Filler Plasticizer Lubricant Material Polyethylene Kaolin (Kaofil, Petroleum oil Zinc stearate.

having a standavg. die. 5 (Shellflex 411,54 ard load melt micron). SS U at 100 F.).

index of 0, a high load melt index of 1.4, and a gearsity of 0.95- Pts. by weight 23.1.: s4 26 1. The substances were thoroughly blended and then worked produce a better image than did photo-sensitive coatings at 400 F. in a B Banbury m xer f r 6 m nut T on a paper base. The dielectric strength of the polyethylmolten miXtufe Was transferred t0 a 2-F011 mill p ene used as a matrix for the photo-sensitive zinc oxide is ing at 350 F., and sheeted out. The sheet, when cooled, high and amply sufficient to Permit the laminam to w ground and Pellefized by PasSi1 1g it through a P cept and hold the electrostatic charge for more than 30 he extruder havmg a W to dlametelbarrel ratlo of seconds in darkness. The charge dissipation factor is rapid, 24/1 and the Screw havmg a compresslon who of 3/1 and total dissipation will occur within half a second when and operating at 325 F. at 50 r.p.m., at an extrusion 25 pressure of 550 psi. The pellets were dried and then fed gi igg 1s exposed to hght through an Ordmary paper through a tubmg extruder havmg a 2 dlameter op Other materials beside kaolin have proved equally saterat'n w't a 0 ml a Extrusion tem erature'was 1 g 1h 3 l g p p 1sfactory as fillers for the substrate, e.g., a composltion 350 F., screw speed, 60 r.p.m. The material passed through a 3 screen pack of 40-6040 mesh at pressures contammg 20% of the Polymer of Example 54% of of 1500 lbs. The hot tubing was blown to film thickness Precipitated calcium carbonate and 26% of the P by the conventional inflati0n" process. Air pressure withticizlng Oil, Process as in Example Performed Substanin the trapped bubble was 0.5" water. Blow point was tially identically A Substrate formed of 15% 0f the P set at 10" above the die. Take-off speed of film was 100 filer 0f EXHIHPIB 0f mined and fiIlClY Plllvfifiled per minute. Film thicknesses of from /2 to 2 mils were vermiculite, and 28% of the plasticizing oil, was equally blown. The film was slit and rolled on cores. satisfactory. The results were equally satisfactory when EXAMPLE II.PREPARATION OF PHOTO-SENSITIVE LAYER Photo-sensitive Polymer material Plastieizer Lubricant Material Polyethylene Photo-sensitive Petroleum oil Zinc stearate.

having a standard zinc oxide (Shellflex 411,

load melt index of (Photox 801, 547 SSU at O, a high load avg. dia. 2 100 F.).

melt index of micron) 1.24 and a density of 0.94-0.95. Pts. by weight; 16.6 71.5 12 1.

1 Total: 101.

The materials were blended in a ribbon mixer and then aluminum silicates and powdered silica gels were used as worked in a B Banbury for 6 minutes at 400 F. The fillers.

molten slug from the Banbury was sheeted out on a 2- EXAMPLE IV roll mill, operating at 350 F. The sheeted product was ground and converted into pellets as in the penetizing An electrosensitive film produced in accord with Exam; step of Example I. The pellets were then fed through a P16 H was lafnmated to f f of 22 bread'wrap tubing extruder and converted to film under the same Paper approxlmalely 0015 lck. The paper and photoconditions as in the film-forming step of Example I. The Sensitive film w pliessed in a platen PYFSS between film was Slit and rolled on corn sheets of aluminum foil at 160 C. for 4 minutes. Good lamination on the paper substrate was secured when the EXMPLE photo-sensitive film thickness was from /z-1 mil. Re-

Prodllcnon of lamlnate productions on the paper-plastic laminate were substan- The substrate film of Example I and the photo-sensitially as good as on the all-plastic laminate, but the meditive film of Example II were cut into sheets and then um was somewhat more sensitive to varying atmospheric placed between films of Mylar or aluminum foil and humidity. If the machine requires electrical conductivity laminated by pressing the sheets for 4 minutes in a platen in the substrateQpaper containing a conductive filler, e.g., press heated to 165 C. Good lamination was secured carbon black, may be substituted for the substrate.

EXAMPLE V.-PRODUGTION OF CONDUOTIVE SUBSTRATE Conductive Polymer material Plasticizer Lubricant Material. Polyethylene Carbon black Petroleum oil Zine ema t having a standard (Vulcan X072, (Shellflex load melt index of Cabot 00., 411, 547 SSU 0, a high load avg. dia. 1 at 100 F.). melt index of march). 1.24 and a density of 0.94-0.95. Pts. by weig 29.8- 22.5- 48.7, 1,

when substantially uniform substrate films and photo- The materials were blended and mixed in a B Banbury sensitive films were each from /21 /2 thousandths inch at 400 F. for 6 minutes. The Banbury batch was transthickness. ferred to a 2-roll mill operating at 350 F. and sheeted out. Subsequently, the sheet was ground and pelletized on EXAMPLE 1X a 1" thermoplastic extruder having a length to diameter barrel ratio of 24/1 and a compression ratio of 3/1 on A sheet as m f by Example 1 11111 In thlckness the screw, and operating at 50 r.p.m. at 325 F.; extruwas adhe'swely lowed to f 2- bread'wrap Paper sion pressures were 550 p.s.i. The pellets were dried and 5 strate which h to vlamlhahoh h been coated Wlth a fed into a 24:1 film extruder equipped with a spread coat of vinylidenechloride copolymer (Daran diameter film die having a 30 mil gap. Extrusion pressure Emu1s1h)- The photo'sehslhve film was Pressed agamst was 1500 p.s.i., temperature 350 F., screw speed '60 the paper by Passing the same throhgh Set of rubber 13pm. A Screen pack of mesh was used. The covered squeeze rolls. The reproduction results were submaterial was reduced to film thickness by the conventional 10 Stahtiahy the Same as those reported in connection with bubble method at a bubble pressure of 0.5" of water. The Example take-off speed was 100" per minute when films of 1-2 mil A photosensitive coating can, with advantage, be

thicknesses were blown. The film was slit and rolled on spread on a Substrate made according to Example I or on cores. one containing any suitable inert filler. Lower hydroscopic In electric discharge (high-speed) printing, the through- 5 sehslhvity as compared to a P p based Sheet Will resistance of the substrate should be as low as possible. obtalhed- Very low resistance values may be secured by extracting EXAMPLE X the plasticizer with a light petroleum solvent. The time of extraction (a few seconds only) may be controlled to produce precise low resistance values.

A sheet prepared according to Example I was extracted by soaking the sheet for 45 seconds in Solvesso #1. The sheet was then dried and subsequently was spread-coated EXAMPLE VI with the following thoroughly-blended mixture.

Sheets of the material of Example V were soaked briefly in a light petroleum solvent to extract the plasticizer. Extraction of the plasticizer for 1 second in Solvesso Weight percent MaterialPhoto-sensitive zinc oxide 83 VehicleVinyl acetate emulsion (Everflex G) Dewey No. 1 reduced the through-resistance of a l-mil film to & Almy of W. Grace 17 approximately 5 ohms. At the same time, extraction conditioned the conductive film to receive and hold the mask- The sheets were dried and then tested in an S.C.M. copier. ing coat. Good reproduction was achieved. Anchorage of the EXAMPLE VII.PREPARATION OF THE MASKING COAT Resin Filler Whitener Solvent Material White shellac Georgia kaolin Titanium dioxide Denatured alcohol.

(DuPont Titanox pigment grade).

A sheet prepared according to Examples V and VI was spread film was excellent when the plasticizer extraction anchored on the bed of a knife-coater and the above mixstep was used.

ture, after being thoroughly stirred and blended, was 40 As a general statement, the photo-sensitive zinc oxide spread on the substrate to a film thickness of .00025. The should constitute as high a proportion as possible of the coating was allowed to dry. total mass of the photo-sensitive layer. Operative results The dry laminate was tested in a high-speed electric will be obtained when the weight proportion of the zinc printer. The white coating burned away in the areas suboxide in the total mixture exceeds 60% and preferably is ject to discharge, leaving a clear black image. Alternate in the approximate range of 70%. formulations for the coating which gave substantially The electrically conductive layers containing carbon equal results in electric discharge printing were composed black should also have as high a proportion of conducof bentonite 20 parts, and 5 parts of a whitener (titanium tive black to polyethylene as is possible, and operative dioxide) suspended in parts of a low molecular weight results will be secured when the weight proportion of caracrylic resin solution. Both roll and knife coating of the 5 bon black to the total mixture exceeds 20%, and preferaabove formulae produced substantially equal results. bly approximately 29%.

EXAMPLE VIIL-PREPARATION OF THE MASKING LAYER Polymer Filler Plasticizer Whitener Material Polyethylene Calcium carbonate Petroleum oil Titanium dioxide having a standard particle size .1- boiling point (DuPont Titanox load melt index of .3 microns greater than pigment grade).

0, a high load (Purecal 0). 300 C. (Shellflex melt index of 1.4 411 547 SSU at and a density of 100 F.).

0.95-0.96. Pts. by weight 20 15 5.

The materials were blended and converted into films fol- The above results cannot be obtained from low-density lowing procedures given in Examples I and II. polyethylene since compositions containing the requisite A laminate was made by sandwiching sheets made acamount of filler material, e.g. zinc oxide or carbon black,

cording to Examples V and VI, /2 mil in thickness, and then are brittle and ditficult to work. When, however, the

sheets from'Example VIII, 1 mil in thickness, between 65 molecular weight of the polyethylene is in excess of 500,- sheets of highly polished Ferrotype Sheets and pressing the 000 and the standard load melt index is substantially 0,

sandwich in a platen press for 4 minutes at 160 C. The workability of the mixture is possible when it is plasticized resulting laminates were tested on a high-speed electric and the high molecular weight imparts sufficient strength, p i t r, d l r, sharply tlined bla k images were even at the high degree of filler loading necessary, to ald d low the material to be sheeted out and subsequently han- Although it is not strictly necessary, the addition of a ti lubricant in the amount of 1% to blends of polyethylene Of e very Wide range of plasticizers which permit and filler given in Examples I, II, V and VIII improves the processibility at these high percentage loadings, any of extrusion characteristics of the blend. A 1 weight percent those such as dibutyl sebacate, asphalt, and others which addition of zinc stearate is recommended. are electrically inert, are suitable. However, the very low cost, excellent electrical characteristics, and easy extractability make petroleum oils especially suited as plasticizers in this invention.

The zinc oxide should be photo-sensitive, and preferably should be sensitized to light in the visible spectrum in known manner by the addition of minor proportions of sensitizing dye. Such zinc oxides are commercially available.

The term electrically responsive as used in this specification and the appended claims is intended to apply to filling materials which are themselves electric conductors such as, e.g., conductive carbon black and substances which accept and hold an electric charge, such as, e.g. photo-sensitive zinc oxide.

When the plasticizer is present, the through-resistance of the combination may be too high to permit use in certain high-speed electric printers, but, as has been described, the resistance can be dropped to very low and predetermined levels by extraction of the plasticizer. Operative through-resistances should be less than 20 ohms, and preferably about ohms. The surface resistance should be less than 2500 ohms. Extraction of the plasticizer has the added advantage that the anchoring of the top coat or top lamination to the substrate is greatly improved.

In instances where a photo-sensitive coat is anchored to a paper substrate, an adhesive bond may be utilized. The adhesive may be rubber cement, polyvinyl acetate, casein, or the like, which is spread on the paper prior to laminating the photo-sensitive coating to the paper substrate. Generally speaking, a wide range of adhesives, provided they are not insulators, and have a through-resistance not in excess of 20 ohms, in the adhesive layer will be found to be practical.

It will be appreciated from the above examples that other methods of joining the two layers may be utilized, e.g. a conductive base coat may be led past the orifice of a slit extruder and the non-conductive white coat may be combined with a conductive substrate by passing the combination between squeeze rolls. A laminated, all-plastic sheet may be made by combining the products of two slit extrusions-one photosensitive and one insensitive. Such changes will readily suggest themselves to one who is familiar with laminating and extrusion techniques and the content of this disclosure.

What is claimed is:

1. Composite copy sheet adapted for use in electric printing apparatus comprising a substrate layer and a coating layer, both of said layers being formed from the milled and sheeted mixture of (a) from -30% by weight of an ethylene polymer having a standard load melt index of zero, and a density lying between 0.93 and 0.96, and (b) from -75% weight percent of a particulate filler, the said filling material in at least one of said layers being a particulate electrically responsive filler substance selected from the class consisting of carbon black and photo-sensing zinc oxide.

2. Composite copy sheet as claimed in claim 1, adapted for use in electrographic printing apparatus comprising a substrate layer composed of the said ethylene polymer and filling material selected from the class of fillers consisting of kaolin, pulverized vermiculite, aluminum silicate, and powdered silica gel, and wherein the upper layer comprises a mixture including the said resin and photo-sensitive zinc oxide.

3. Copy sheet as claimed in claim 2 wherein the proportion of zinc oxide in the top lamination is about 71%.

4. Copy sheet as claimed in claim 1 wherein the substrate layer is formed of the said resinous composition and approximately 22 /2% of carbon black and wherein the said top layer is a masking coat comprising the said resinous composition and a white pigment.

5. The process of preparing image sheets suitable for use in electrographic reproduction apparatus which comprises milling from 15-30 parts by weight of an ethylene polymer having a standard load melt index of zero, and a density lying between 0.93 and 0.96, and from 20-75 parts by weight of photo sensitive zinc oxide, and from 10-50 parts by weight of a plasticizer, forming the milled mixture into sheets, preparing a second composition containing the said resin in proportions of from 15-30 parts by weight, and from 20-75 parts by weight of a filler selected from the class of filling substances consisting of kaolin, calcium carbonate, pulverized vermiculite, aluminum silica, and silica gel, and from 10-50 parts by weight of a plasticizer, forming the said composition into a sheet and laminating the first and the second named sheets together by heat and pressure to form the photo-sensitive reproduction medium.

6. The process of preparing image sheets suitable for use in electric printer apparatus which comprises forming a sheet of from 15-30 parts by weight of an ethylene polymer having a standard load melt index of zero, and a density lying between 0.93 and 0.96, and from 20-75 parts by weight of a white pigment comprising calcium carbonate and titanium dioxide, forming a second named sheet from the said resin and from 20-29% of electrically conductive carbon black and a plasticizer, and laminating the first and second named sheets together by heat and pressure to form an image sheet suitable for high-speed electric printing.

7. That process of adjusting the through electrical resistance of image sheets produced according to claim 6,- which includes extracting the plasticizer from the said second named sheet with a petroleum solvent prior to laminating the first and second sheets together, whereby the through resistance of the second sheet is reduced to values of less than 20 ohms.

References Cited UNITED STATES PATENTS WILLIAM L. JARVIS, Primary Examiner Us. c1. X.R. 

